The present invention relates to method and apparatus for separating carbon product from used tire. More particularly, the present invention relates to highly efficient method and apparatus for decomposing used tires using specific wavelength ranges of microwave in non-reacting environment.
With wide and ever increasing use of automobiles, proper disposal of used tires has become important. Currently, about 3 billion used tires are waiting for disposal in USA and it is estimated that about two hundred million used tires are generated every year (Korea Tire Manufacturers Association). A tire is mainly composed of synthetic polymer materials, and the calorific value is about 34 MJ/kg, which is greater than 29 MJ/kg, the reference calorific value of coal. Typical composition of a tire excluding the iron core and fabric is styrene-butadiene copolymer 43.5 wt %, carbon black 32.6 wt %, oil 21.7 wt %, and additives 2.2 wt %, which includes sulfur and zinc oxide.
For environmental reasons, combustion of tires is prohibited since it produces many pollutants. Recycling methods for tires other than combustion include a recycled tire, recycled rubber, an artificial fishing bank, a buffer, etc. Processes for fueling of tire include breaking, direct burning and extracting fuel. Direct burning of tire includes burning solely tire, burning mixture of tire with coal or oil, and fuel for burning cement.
Method of extracting fuel includes liquefying and thermal decomposition. Liquefying tire is similar to liquefying coal and has less than 0.1% sulfur in the produced fuel liquid. Thermal decomposition of tire includes heating tire at relatively low temperature and it is possible to recover oil, gas, carbon and dry distillation residue. The calorific value of extracted fuel oil is 33 MJ/kg, which is similar to that of A grade heavy oil, and the recovered carbon may be used as carbon black and activated charcoal.
Dry distillation processes of tire by prior art are classified into two categories, direct heating and indirect heating. Referring to FIG. 1, the direct heating method blows combustion gas from a burner 110 directly into a reaction furnace 112. Efficiency is better than the indirect heating method since the combustion gas directly contacts the used tires 114. However since excessive amount of oxygen is also injected into the reaction furnace, there is possibility of explosion with the vaporized oil inside the furnace. Also substantial amount of water, and carbon generated through reaction of rubber and oxygen are mixed with the product thereby degrading the quality of the oil.
Referring to FIG. 2, the indirect heating method heats used tires, which are stacked and isolated from outside, from outside. The heated tires decompose at high temperature and produce gaseous oil, which is cooled and collected in liquid state. Part of the recovered oil is used for supplying energy for thermal decomposition of tires. The disadvantages are that the heating efficiency is very low and most of the recovered oil is used up for heating the furnace, and the heating efficiency becomes worse as the size of the reaction furnace becomes bigger.